make needless_return work with void functions

clippy_lints/src/returns.rs

@@ -83,6 +83,12 @@ declare_clippy_lint! {
     "needless unit expression"
 }
 
+#[derive(PartialEq, Eq, Copy, Clone)]
+enum RetReplacement {
+    Empty,
+    Unit
+}
+
 declare_lint_pass!(Return => [NEEDLESS_RETURN, LET_AND_RETURN, UNUSED_UNIT]);
 
 impl Return {
@@ -91,7 +97,7 @@ impl Return {
         if let Some(stmt) = block.stmts.last() {
             match stmt.node {
                 ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => {
-                    self.check_final_expr(cx, expr, Some(stmt.span));
+                    self.check_final_expr(cx, expr, Some(stmt.span), RetReplacement::Empty);
                 },
                 _ => (),
             }
@@ -99,13 +105,13 @@ impl Return {
     }
 
     // Check a the final expression in a block if it's a return.
-    fn check_final_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr, span: Option<Span>) {
+    fn check_final_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr, span: Option<Span>, replacement: RetReplacement) {
         match expr.node {
             // simple return is always "bad"
-            ast::ExprKind::Ret(Some(ref inner)) => {
+            ast::ExprKind::Ret(ref inner) => {
                 // allow `#[cfg(a)] return a; #[cfg(b)] return b;`
                 if !expr.attrs.iter().any(attr_is_cfg) {
-                    self.emit_return_lint(cx, span.expect("`else return` is not possible"), inner.span);
+                    self.emit_return_lint(cx, span.expect("`else return` is not possible"), inner.as_ref().map(|i| i.span), replacement);
                 }
             },
             // a whole block? check it!
@@ -117,32 +123,61 @@ impl Return {
             // (except for unit type functions) so we don't match it
             ast::ExprKind::If(_, ref ifblock, Some(ref elsexpr)) => {
                 self.check_block_return(cx, ifblock);
-                self.check_final_expr(cx, elsexpr, None);
+                self.check_final_expr(cx, elsexpr, None, RetReplacement::Empty);
             },
             // a match expr, check all arms
             ast::ExprKind::Match(_, ref arms) => {
                 for arm in arms {
-                    self.check_final_expr(cx, &arm.body, Some(arm.body.span));
+                    self.check_final_expr(cx, &arm.body, Some(arm.body.span), RetReplacement::Unit);
                 }
             },
             _ => (),
         }
     }
 
-    fn emit_return_lint(&mut self, cx: &EarlyContext<'_>, ret_span: Span, inner_span: Span) {
+    fn emit_return_lint(&mut self, cx: &EarlyContext<'_>, ret_span: Span, inner_span: Option<Span>, replacement: RetReplacement) {
-        if in_external_macro(cx.sess(), inner_span) || in_macro_or_desugar(inner_span) {
+        match inner_span {
-            return;
+            Some(inner_span) => {
-        }
+                if in_external_macro(cx.sess(), inner_span) || in_macro_or_desugar(inner_span) {
-        span_lint_and_then(cx, NEEDLESS_RETURN, ret_span, "unneeded return statement", |db| {
+                    return;
-            if let Some(snippet) = snippet_opt(cx, inner_span) {
+                }
-                db.span_suggestion(
+
-                    ret_span,
+                span_lint_and_then(cx, NEEDLESS_RETURN, ret_span, "unneeded return statement", |db| {
-                    "remove `return` as shown",
+                    if let Some(snippet) = snippet_opt(cx, inner_span) {
-                    snippet,
+                        db.span_suggestion(
-                    Applicability::MachineApplicable,
+                            ret_span,
-                );
+                            "remove `return` as shown",
+                            snippet,
+                            Applicability::MachineApplicable,
+                        );
+                    }
+                })
+            },
+            None => {
+                match replacement {
+                    RetReplacement::Empty => {
+                        span_lint_and_then(cx, NEEDLESS_RETURN, ret_span, "unneeded return statement", |db| {
+                            db.span_suggestion(
+                                ret_span,
+                                "remove `return`",
+                                String::new(),
+                                Applicability::MachineApplicable,
+                            );
+                        });
+                    }
+                    RetReplacement::Unit => {
+                        span_lint_and_then(cx, NEEDLESS_RETURN, ret_span, "unneeded return statement", |db| {
+                            db.span_suggestion(
+                                ret_span,
+                                "replace `return` with the unit type `()`",
+                                "()".to_string(),
+                                Applicability::MachineApplicable,
+                            );
+                        });
+                    }
+                }
             }
-        });
+        }
     }
 
     // Check for "let x = EXPR; x"
@@ -195,7 +230,7 @@ impl EarlyLintPass for Return {
     fn check_fn(&mut self, cx: &EarlyContext<'_>, kind: FnKind<'_>, decl: &ast::FnDecl, span: Span, _: ast::NodeId) {
         match kind {
             FnKind::ItemFn(.., block) | FnKind::Method(.., block) => self.check_block_return(cx, block),
-            FnKind::Closure(body) => self.check_final_expr(cx, body, Some(body.span)),
+            FnKind::Closure(body) => self.check_final_expr(cx, body, Some(body.span), RetReplacement::Empty),
         }
         if_chain! {
             if let ast::FunctionRetTy::Ty(ref ty) = decl.output;

tests/ui/needless_return.rs

@@ -1,5 +1,9 @@
 #![warn(clippy::needless_return)]
 
+macro_rules! the_answer {
+    () => (42)
+}
+
 fn test_end_of_fn() -> bool {
     if true {
         // no error!
@@ -36,6 +40,22 @@ fn test_closure() {
     let _ = || return true;
 }
 
+fn test_macro_call() -> i32 {
+    return the_answer!();
+}
+
+fn test_void_fun() {
+    return;
+}
+
+fn test_void_if_fun(b: bool) {
+    if b {
+        return;
+    } else {
+        return;
+    }
+}
+
 fn main() {
     let _ = test_end_of_fn();
     let _ = test_no_semicolon();

tests/ui/needless_return.stderr

@@ -1,5 +1,5 @@
 error: unneeded return statement
-  --> $DIR/needless_return.rs:8:5
+  --> $DIR/needless_return.rs:12:5
    |
 LL |     return true;
    |     ^^^^^^^^^^^^ help: remove `return` as shown: `true`
@@ -7,46 +7,70 @@ LL |     return true;
    = note: `-D clippy::needless-return` implied by `-D warnings`
 
 error: unneeded return statement
-  --> $DIR/needless_return.rs:12:5
+  --> $DIR/needless_return.rs:16:5
    |
 LL |     return true;
    |     ^^^^^^^^^^^^ help: remove `return` as shown: `true`
 
 error: unneeded return statement
-  --> $DIR/needless_return.rs:17:9
+  --> $DIR/needless_return.rs:21:9
    |
 LL |         return true;
    |         ^^^^^^^^^^^^ help: remove `return` as shown: `true`
 
 error: unneeded return statement
-  --> $DIR/needless_return.rs:19:9
+  --> $DIR/needless_return.rs:23:9
    |
 LL |         return false;
    |         ^^^^^^^^^^^^^ help: remove `return` as shown: `false`
 
 error: unneeded return statement
-  --> $DIR/needless_return.rs:25:17
+  --> $DIR/needless_return.rs:29:17
    |
 LL |         true => return false,
    |                 ^^^^^^^^^^^^ help: remove `return` as shown: `false`
 
 error: unneeded return statement
-  --> $DIR/needless_return.rs:27:13
+  --> $DIR/needless_return.rs:31:13
    |
 LL |             return true;
    |             ^^^^^^^^^^^^ help: remove `return` as shown: `true`
 
 error: unneeded return statement
-  --> $DIR/needless_return.rs:34:9
+  --> $DIR/needless_return.rs:38:9
    |
 LL |         return true;
    |         ^^^^^^^^^^^^ help: remove `return` as shown: `true`
 
 error: unneeded return statement
-  --> $DIR/needless_return.rs:36:16
+  --> $DIR/needless_return.rs:40:16
    |
 LL |     let _ = || return true;
    |                ^^^^^^^^^^^ help: remove `return` as shown: `true`
 
-error: aborting due to 8 previous errors
+error: unneeded return statement
+  --> $DIR/needless_return.rs:44:5
+   |
+LL |     return the_answer!();
+   |     ^^^^^^^^^^^^^^^^^^^^^
+
+error: unneeded return statement
+  --> $DIR/needless_return.rs:48:5
+   |
+LL |     return;
+   |     ^^^^^^^ help: remove `return`
+
+error: unneeded return statement
+  --> $DIR/needless_return.rs:53:9
+   |
+LL |         return;
+   |         ^^^^^^^ help: remove `return`
+
+error: unneeded return statement
+  --> $DIR/needless_return.rs:55:9
+   |
+LL |         return;
+   |         ^^^^^^^ help: remove `return`
+
+error: aborting due to 12 previous errors